1. Field of the Invention
The present invention relates to a high-frequency micro-electro mechanical system (hereinafter, xe2x80x9cMEMSxe2x80x9d), and more particularly, to an MEMS switch having a single anchor.
2. Description of the Related Art
An MEMS switch is a switch that is commonly adopted for signal routing or impedance matching networks in a wire communication system that uses microwave or millimeter wave.
In the existing monolithic microwave integrated circuits, a radio frequency (RF) switch is realized mainly with GaAs FET or a pin diode. However, the use of these elements causes a considerable insertion loss when the RF switch is switched on, and deteriorates signal separation characteristics when the RF switch is switched off.
To improve these problems, much research is made on developing various MEMS switches, and further, a tremendous increase in Mobile communication phone markets increases the importance of the MEMS switches. As a result, a variety of MEMS are suggested.
FIG. 1 is a plan view of a conventional MEMS switch. Referring to FIG. 1, a moving plate 10 is bilateral symmetry, being placed across input-output transmission lines 12 and 14 and a grounding line 16, as shown in FIG. 2. Referring to FIG. 2, the input-output transmission lines 12 and 14 are installed on a substrate S to be distant away from each other, and the moving plate 10 is placed over these input-output transmission lines 12 and 14.
Here, reference numerals 18 and 20 denote first and second anchors for holding the moving plate 10. The first and second anchors 18 and 20 are symmetrical with regard to the input-output transmission lines 12 and 14, and connected to the both ends of the moving plate 10 via first and second springs 22 and 24, respectively. Due to this structure, with the first and second anchors 18 and 20 as holding points, the moving plate 10 is in contact with the input-output transmission lines 12 and 14 by a driving electrode (not shown) when a driving force is given to the moving plate 10, and returns back to the original position when the driving force is canceled from the moving plate 10.
FIG. 3 is a cross-sectional view of the conventional MEMS switch of FIG. 1, taken along the line 3-3xe2x80x2. Referring to FIG. 3, first and second driving electrodes 26 and 28 are installed between the first and second anchors 18 and 20, and actuate the moving plate 10 to be in contact the first and second anchors 18 and 20. The first and second driving electrodes 26 and 28 are separated from each other at a predetermined interval.
Although not shown in the drawings, the input-output transmission lines 12 and 14 and the grounding line 16 are positioned between the first and second driving electrodes 26 and 28.
Referring to FIGS. 1 and 2, the conventional MEMS switch has the moving plate 10 across the input-output transmission lines 12 and 14 and the grounding line 16. Thus, when the moving plate 10 is actuated, it comes in contact with the grounding line 16, which causes the leakage of a transmitted signal. Also, the both ends of the moving plate 10 are fixed by the first and second anchors 18 and 20. For this reason, the moving plate 10 may transform upward and downward in the event that it thermally expands. A change in the shape of the moving plate 10 may increase driving voltage or power consumption when the MEMS switch is turned on.
To solve the above-described problems, it is an object of the present invention to provide an MEMS switch capable of preventing an increase in driving voltage due to the leakage of a transmitted signal or the transformation of a moving plate, or power consumption when the MEMS switch is on.
Accordingly, to achieve the above object, there is provided an MEMS switch including: a substrate; grounding lines installed on the substrate to be distant away from each other; signal transmission lines positioned at predetermined intervals between the grounding lines; an anchor placed between the signal transmission lines; a driving electrode not being in contact with the anchor, the signal transmission lines and the grounding lines, the driving electrode for encircling the anchor; and a moving plate positioned on the driving electrode to be overlapped with portions of the signal transmission lines, the moving plate connected to the anchor elastically.
Here, the moving plate is connected to the anchor via springs, and the moving plate and the anchor are connected to each other via four planar springs.
Preferably, the width of the moving plate perpendicular to the grounding lines is the same as the widths of the signal transmission lines.
Preferably, the driving electrode is geometrically shaped the same as the moving plate.
One end of each of the four planar spring is connected to the four corners of the anchor, but the one end of each plate spring is connected to one of two surface consisting of each corner, and the other end of each planar spring is extended from the one end along the surface of the anchor, to which the one end is connected, to connect to the inner surface of the moving plate which is opposite to the other surface of the anchor adjacent to the surface to which the one end is connected.
In an MEMS switch according to the present invention, a moving plate is positioned between grounding lines such that it can be actuated not in contact with these grounding lines. Thus, the MEMS switch according to the present invention is capable of completely transmitting a signal even if the moving plate comes in contact with the grounding lines, or these grounding lines are broken or become narrow. Also, the moving plate is hold by a single anchor, and thus, it is possible to prevent deformation of the moving plate upward and downward even if a substrate expands due to heat from the outside. Therefore, power consumption can be prevented when driving voltage for actuating the moving plate increases or the MEMS switch is switched on.